Serena Williams (1) vs. Li Na (5)
There can't be many instances of a women's grand slam quarterfinal finishing 6-0 6-0, but that is exactly what happened when Serena Williams beat Carla Suarez Navarro in her last match. It's tempting to make Serena the overwhelming favourite to win on the back of such a performance, but Li is a big step up compared to all her previous opponents. Li did go into her shell in the quarterfinal against Ekaterina Makarova, after playing some fantastic aggressive tennis in the tournament up to that point. Even though Serena has an 8-1 lead in their career head-to-head, the last three matches have been extremely close, including a 7-5 7-5 win for Serena in Cincinnati last month. The close nature of that scoreline indicates the huge task that Li faces in breaking the best serve in women's tennis. Li will give it her all, and if she attacks more often, she might have a window of opportunity. Unfortunately for her, its more likely that she will be under constant pressure to hold her serve, and when push comes to shove Serena will ram home the advantage against Li.Flavia Pennetta vs. Victoria Azarenka (2)
After three quarterfinal exits at the US Open, it is great to see Flavia Pennetta finally make the semifinals. Pennetta has been in superb form, not dropping a set en route to the semis despite playing against numerous seeded players. Pennetta is moving beautifully to cover all areas of the court, and her net play has been almost flawless. Azarenka on the other hand hasn't been at her best so far, although they were signs she was regaining form in her quarterfinal win over Daniela Hantuchova. She still has to sort out some issues with her serve, but Azarenka has relied on touch and defence, including a new backhand drop shot that has set up many points for her when her aggressive shots from the baseline have failed her. I think this match can possibly go three sets, especially if Pennetta maintains her baseline consistency and rushes Azarenka. However, the world number two has added a much-needed resilience to her game, and that should see her through a potentially terrific contest.